Cable Size Calculator — South Africa
Find the correct cable size for any SA circuit. Checks current carrying capacity and voltage drop against SANS 10142 requirements.
⚡ Quick fill — tap a common circuit:
⚠️ For planning purposes only. All electrical work in SA must be carried out by a registered electrician under SANS 10142. A Certificate of Compliance (CoC) is required.
Cable Sizing in South Africa — SANS 10142 Explained
Selecting the correct cable size is one of the most critical steps in any electrical installation. An undersized cable overheats, degrades insulation, creates a fire risk, and will fail a Certificate of Compliance (CoC) inspection. Oversizing wastes money unnecessarily. SANS 10142 — South Africa's wiring code — specifies exactly how cable sizing must be done.
There are two separate tests a cable must pass under SANS 10142, and both must be satisfied independently. This calculator checks both automatically.
The Two SANS 10142 Cable Sizing Checks
Check 1 — Current Carrying Capacity
Every cable has a maximum continuous current it can carry safely without the insulation overheating. For standard copper PVC-insulated cables at 70°C operating temperature, these are the rated values used in South Africa:
| Cable Size | Clipped Direct (A) | In Conduit (A) | Volt Drop (mV/A/m) | Typical Use |
|---|---|---|---|---|
| 1.5mm² | 17.5A | 14A | 28.0 | Lighting circuits |
| 2.5mm² | 25A | 20A | 17.0 | Plugs, geysers (short runs) |
| 4mm² | 32A | 26A | 11.0 | Geysers, cooktops (short runs) |
| 6mm² | 41A | 34A | 7.1 | Stoves, pool pumps |
| 10mm² | 57A | 46A | 4.2 | Large stoves, sub-mains |
| 16mm² | 75A | 61A | 2.7 | Sub-distribution boards |
| 25mm² | 100A | 80A | 1.7 | Main DB feeds |
| 35mm² | 125A | 100A | 1.3 | Main supply cables |
Source: MicCom Cables SA / SANS 10142 aligned. Values for copper PVC-insulated cables, conductor operating temperature 70°C.
Check 2 — Voltage Drop
Even if a cable can carry the current safely, it must not drop too much voltage along its length. SANS 10142 sets the maximum voltage drop at 5% of the supply voltage for final circuits:
- 230V single phase: Maximum 11.5V drop
- 400V three phase: Maximum 20V drop
Current (A) = Power (W) ÷ Voltage (V) [single phase]
Current (A) = Power (W) ÷ (400 × 1.732) [three phase]
Voltage Drop (V) = mV/A/m × Current (A) × Length (m) ÷ 1000
VD % = Voltage Drop (V) ÷ Supply Voltage (V) × 100
SANS 10142 limit = 5% of supply voltage (11.5V / 20V)
Why Installation Method Matters
A cable installed in conduit or enclosed trunking cannot dissipate heat as efficiently as one clipped to a surface or run in open air. This means the same cable has a lower current rating in conduit than when surface-mounted. The SANS 10142 derating for conduit is significant — a 2.5mm² cable drops from 25A (clipped) to 20A (in conduit). Failing to apply this derating results in overloaded cables that overheat and degrade.
Common SA Circuit Examples
These are typical cable sizes used in South African residential installations. Always verify with a registered electrician, as actual installations depend on run length, grouping, and ambient temperature.
- Lighting circuits: 1.5mm² (up to 20m runs), 2.5mm² for longer runs
- 15A plug circuits: 2.5mm² (short runs), 4mm² (over 25m)
- Geyser 3kW: 2.5mm² (under 15m), 4mm² (15–30m)
- Electric stove 6–9kW: 6mm² minimum, 10mm² for longer runs
- Air conditioner 3–5kW: 2.5mm² (short runs), 4mm² (over 15m)
- DB board sub-mains: 10mm²–25mm² depending on total load
- Inverter / solar feed: 10mm²–25mm² depending on inverter size and run length